The Early Cainozoic climate, beginning approximately 65 million years
ago, was completely different than it is today.

During the Time of Dinosaurs

During the late Jurassic to mid-Cretaceous Period the Australian continent
was covered with shallow seas. Probably because the high, humid temperatures
(possibly as high as 10degrees Celsius higher than our own!) which existed
when the dinosaurs ruled the world. The glaciers had melted and the seas
had risen accordingly creating a hot humid existence. Perfect for cold-blooded
reptiles. Plesiosaurs swam in the warm shallow seas of central Australia.

145.6 - 65 million years ago. During the Cretaceous period Australia was
hot and basically separated up into a number of landmasses separated by
great shallow seas. That is why many of Australia's dinosaurs were sea-living
beasts like Plesiosaurs and Ichthyosaurs.

65
- 23.3 million years ago. The forests were more temperate and water still
covered much of the country with lakes and rivers. Great lush forests
fed and protected large numbers of animals that were dependent on it for
food and shelter. Where desert and arid conditions exist now the country
might have looked more like today's tropical Queensland rainforest.

About 23 million years ago Australia broke away from Antarctica and moved
northwards. It was during this last 23 million years that Australia gained
all its tropical plants and animals. During the last 5 million its arid
centre developed. Rainfall giving way top Spinifex grasses.

12 -15 million years ago the Australian Plate collided with the Pacific
plate near New Guinea causing a great deal of pushing, shoving and general
mountain building in New Guinea.

Animals and plants were able to migrate from the north to Australia which
had been isolated so long. By the end of the cretaceous the earth's climate
was beginning to cool once again and Australia was once again closer to
the Antarctic Circle. The Antarctic was a lot milder than it is today
but soon all that was to change. Ice was beginning to form at the poles
again. Water was taken from the seas and cold currents disrupted previously
warm marine feeding grounds. The world was still warm but a lot drier
than it had been before.

During the last 1.64 million years the lush forests gave way to the grasses,
which opened out the now drier continent. Animals which thrived in the
forests or only ate leaves were disadvantaged by those that took to eating
grasses. Fish stocks in the seas probably dwindled as the seas cooled,
and the large dominant birds declined.
The polar icecaps grew, water decreased and the land began to look like
it does now. The central Australian lakes dried up and at about 20,000
years ago the country was even drier and dustier than it is now.